This invention relates generally to liquid metering and transfer valves for use in a diluting system and more particularly provides a liquid metering and transfer valve assembly of the rotary type for measuring and delivering at least three precise microliter volumes of a liquid sample along with respective predetermined volumes of a diluent to different preselected destinations and employing a single aspiration or loading step.
Reference has been made to U.S. Pat. Nos. 4,445,391 and 4,152,391. The liquid transfer valves provided in these patents preferably comprise a pair of stationary valve disc elements sandwiching a center rotatable valve disc element, said elements arranged coaxially with the faces of the center element frictionally sealingly engaged with the adjacent faces of the stationary elements. These valves have achieved considerable commercial success and included internal passageway means of precise interior volume to provide a precise volume of a single liqud sample for dilution. The segmenting passageway means were provided in the center, movable valve disc of the valve assembly. In both patents there was provided an external loop to provide a precise volume of liquid sample different from the measured volume provided by the interior segmenting passageway means. In the valve of U.S. Pat. No. 4,152,391, the external loop was connected to the center movable valve disc element and passed through a suitable slot formed in one of the stationary valve disc elements so that the center valve disc element could be rotated. In the valve of U.S. Pat. No. 4,445,391, the external loop was connected to one of the stationary valve disc elements and coupled to second passageway means formed in the center valve disc element. In both patented valve assemblies, external connections for feed of diluent and for coupling to lines leading to predetermined locations or destinations were made to the outer, stationary valve disc elements of said valve assemblies. The valve assembly of the U.S. Pat. No. 4,152,391 also required interior galleries to define several of the liquid paths therethrough.
The valve assembly of the U.S. Pat. No. 4,445,391 was less complex in construction than that of the U.S. Pat. No. 4,152,391, providing the external loop coupled in series with the segmenting passageway means rather than parallel thereto. This meant that the loading step of the valve assembly of the U.S. Pat. No. 4,152,391, particularly if three dilutions were desired required a Y path or at least two aspiration steps during the loading condition. The U.S. Pat. No. 4,445,391 valve assembly was less costly to manufacture than the valve assembly of the U.S. Pat. No. 4,152,391. Sample volume was reduced. Interior galleries found in the U.S. Pat. No. 4,152,391 were eliminated in the U.S. Pat. No. 4,445,391 valve assembly. Of advantage with the U.S. Pat. No. 4,152,391 valve assembly was the provision of means whereby a dilution, in addition to the two dilutions provided by the U.S. Pat. No. 4,445,391 valve assembly, could be provided, although the sampling paths provided for the second and third liquid sample volumes were in parallel and the valve assembly required a pair of arcuate slots in the one stationary valve disc element and further required a pair of internal gallery formations. More important, the third volume could not be obtained during the same aspiration or loading step and required a "one/or the other" selection. The two patented valve assemblies were appreciably different in structure so that one could not convert one structure into the other without substantial change nor could one structure be replaced with the other without change in operation of the instrument. The valve assembly of the U.S. Pat. No. 4,445,391 could not be remodeled by following the teachings of U.S. Pat. No. 4,152,391 in an effort to provide three measured volumes of liquid sample for forming three dilutions without drastic and uneconomical alterations in the structure of the U.S. Pat. No. 4,445,391 valve assembly. Capability of retrofit of a valve assembly capable of providing three dilutions on a single loading in instruments in which the U.S. Pat. No. 4,445,391 valve assembly is installed would be of considerable advantage.
Accordingly, it has become desirous to provide for delivery of three separate dilutions from a single valve assembly without drastic alterations of the structure of the U.S. Pat. No. 4,445,391, to provide therein means defining a series path through the valve assembly to enable use of a single aspiration or loading step to introduce liquid sample through all the measuring portions of the valve assembly and yet to retain all the advantages of the U.S. Pat. No. 4,445,391 patented valve assembly.
Further, it would be of considerable advantage, notwithstanding the paucity of available space, to incorporate in a valve assembly capable of providing three dilutions, means to prevent any material from escaping from any internal passageway junctions and traveling to the outer circumferential surface of the valve assembly.